The relay technique acts as an emerging technique, which attracts more extensive attention, and is considered as a key technique of the B3G/4G. Since wireless communication or cellular system in the future is required to increase the coverage range, and to support higher speed transmission, which puts forward a new challenge to the wireless communication technique. At the same time, the cost problem of constructing and maintaining the system becomes more outstanding. With the transmission speed and communication distance increasing, the energy consumption problem of the battery also becomes outstanding, and wireless communication in the future will use the higher frequency, which cause more serious path loss attenuation. By the relay technique, the traditional single-hop link is divided into a plurality of multi-hop links, and since the distance is decreased, the path loss is reduced greatly, which contributes to improving the transmission quality and extending the communication range, and thereby providing faster and better services for users.
In the relay network, a link between a user that the relay station participates in serving and the relay station is called an Access Link, a link between a relay station and a base station is called a Backhaul Link, and a user that the base station participates in serving and the base station is called a Direct Link, as shown in FIG. 1.
When a user locates in the joint coverage range of the base station and the relay station, a cooperative communication method can be used to make the base station and the relay station serve the user together, and thus improving the system capacity and the resources utilization efficiency, as shown in FIG. 2.
Relay station downlink cooperative retransmission is a relay network cooperative communication mode, and when this mode is used, and when the relay station has a receiving error only in the downlink transmission of the first transmission subframe in the Direct Link and the transmitter is required to carry out the retransmission, the corresponding downlink retransmission transmitting is carried out in the retransmission subframe in the Access Link to improve the transmission success rate of the downlink retransmission. Relay station downlink cooperative retransmission is a cooperative mode of small overhead, good compatibility and nearly no modification being necessary to the existing system, as shown in FIG. 3.
However, when the relay station carries out the cooperative retransmission on the downlink data in the Direct Link, such a case may be encountered: in the retransmission subframe, since the number of wireless resources occupied by the Physical Downlink Control Channel (PDCCH) varies compared with the first transmission subframe, which causes that the number of available wireless resources during retransmitting data is different from that during the first transmission, and that means the retransmission transmitter is required to carry out corresponding adjustment in the physical layer processing to match the available wireless resources in the current retransmission subframe. However, the relay station does not know what kind of variance occurs on the number of available wireless resources during the retransmission of data, and is unable to carry out the corresponding physical layer processing normally during the retransmission transmitting, which may cause the interference among the retransmission signals or a waste of the wireless resources, and even the retransmission failure, and the system performance is reduced, as shown in FIG. 4.
A method currently put forward to solve the above problem is that the base station notifies the relay station how to carry out the retransmission transmitting by the control signaling in a certain control subframe in advance, or notifies the available wireless resources status in the retransmission subframe to the relay station, and then the relay station carries out the corresponding physical layer processing on the Transport Block (TB) which requires retransmitting according to the control signaling received from the base station, and carries out the cooperative retransmission transmitting in the retransmission subframe, as shown in FIG. 5.
The drawback in the above method is that the base station is required to send the control signaling to the relay station before the cooperative retransmission transmitting, which introduces extra overhead; and the relay station is required to receive this control signaling in a certain control subframe, and since the self interference should be avoided, this control subframe is unable to be configured as other user's cooperative retransmission subframe, which severely affects the flexibility of the subframe configuration; besides, the base station is required to start to generate the control signaling and carry out the transmitting after determining the available wireless resources status in the retransmission subframe, and the relay station is also required to carry out the corresponding physical layer processing process after receiving and correctly analyzing the control signaling from the base station and finally carry out the retransmission transmitting, which will bring a lot of time delay, and severely reduce the service quality and resources utilization efficiency.